1. Field of the Invention
The present invention relates to a semiconductor module with a semiconductor chip contained in a package, and more particularly to the semiconductor module capable of preventing dew condensation in the package.
2. Description Related to the Prior Art
Digital cameras and Camera phones are provided with image sensor modules. The image sensor module has a package which contains an image sensor chip so as to protect a light receiving surface of the image sensor chip from dusts. Generally, the package is made of either plastic, metals, or ceramic, and the plastic is often used in these days because of ease of process and low cost.
The package has a package body and a cover. Formed in the package body is a chip chamber, in which the image sensor is contained. The transparent cover is placed on the package body and bonded thereto with an adhesive agent such as an epoxy resin. In this manner, the chip chamber is sealed for the protection from dusts.
The semiconductor chips such as the image sensors are often made of an epoxy resin because of cost concerns. The epoxy resin, nevertheless, absorbs moisture when left in a damp place for a long time, and sometimes causes dew condensation in the chip chamber that contains the semiconductor chip. The Japanese patent laid-open publication No. 2004-331920 then discloses the semiconductor chip package made of a waterproof, low water absorption material.
Even with such waterproof package, however, if water vapor happens to be trapped in the chip chamber when the semiconductor chip is sealed, there is no method for releasing the water vapor from the chip chamber. As a result, when the ambient temperature goes lower than the temperature inside the chip chamber, dew condensation occurs in the chip chamber. In this case, the dew drops may fall on the semiconductor chip and cause a short circuit in the semiconductor chip. Furthermore, if the semiconductor chip is the image sensor chip, a light receiving surface of the image sensor may have the dew condensation, and the quality of images may therefore be degraded.